The Complete Handbook of Bicycle Tires

Chapter 1: Understanding Bicycle Tires

A bicycle tire is a structural membrane under tension. It is not a simple rubber band wrapped around a wheel. It has to manage several opposing forces simultaneously: it must flex enough to absorb road vibration, yet be rigid enough to resist deformation under cornering and braking loads. It must be light enough to accelerate quickly, yet strong enough to withstand impacts from potholes and curbs. And it must grip the ground to translate your pedaling force into forward motion, which requires a balance between the compounds on its surface and the deformation of its casing against the pavement.

To understand how this works in practice, picture a standard clincher tire, the type found on most road, hybrid, and mountain bikes. When inflated, the tire maintains its shape because the air pressure inside is working against the tension of the casing's fibers. The casing is the tire's skeleton, usually woven from nylon, polyester, or cotton threads. The density of these threads is measured in TPI, or Threads Per Inch. A higher TPI casing (for example, 120 TPI) uses thinner, more densely packed fibers. This allows the casing to be more flexible, which reduces rolling resistance on smooth surfaces, because the tire conforms more easily to the road, and the sidewalls flex more naturally with the road surface. A lower TPI casing (like 60 TPI) is built with thicker, more widely spaced threads. It is more resistant to punctures and sidewall cuts, but it feels stiffer